Method of granulating raw material for sintering, and method of manufacturing sintered iron ore

ABSTRACT

A raw material for sintering of 100% in total is blended so as to adjust iron-containing dust and/or sludge to 60% or more, and coarse grains having a grain size of 2 mm or larger to 20% or more on the weight basis, one-third or less of the total amount of addition of coke breeze is added as a fuel, the blend is kneaded and granulated using a vibration kneading granulator to thereby produce granulated grains, the residual portion of the total amount of addition of coke breeze is added to the granulated grains, the blend is subjected to exterior coating granulation using a rolling type granulator, thus-granulated raw material for sintering is screened, and a fraction having a grain size of 1 mm or larger is used for sintering, making it possible to sinter microparticulate dust and microparticulate sludge as main raw materials, which have conventionally been used only to a limited amount of use.

TECHNICAL FIELD

The present invention relates to a method of granulating raw materialfor sintering using microparticulate dust and microparticulate sludge asmain raw materials, and a method of manufacturing sintered iron oreusing the raw material for sintering granulated by the method ofgranulating raw material for sintering.

BACKGROUND ART

Dust and sludge produced as by-product in the individual processes ofiron making, steel making, casting, rolling, machining and so forth atironworks contain a large fraction having a grain size of as fine asseveral tens of micrometers or smaller, wherein a part of which isrecycled as being used for sintering which employs usually iron orepowder as a main raw material.

The microparticulate dust and microparticulate sludge, however, mayobstruct gas permeability and fusing performance in the process ofsintering, and therefore only a limited amount of use is allowable. Theymay be used only to as much as several percent even if they were used asbeing mixed with iron ore powder, and may be recycled only to as much as10% or around even if the granulation thereof were enhanced typically bymini-pelletizing.

On the other hand, some of the microparticulate dust andmicroparticulate sludge contain impurities such as zinc, alkali, oilsand so forth. These impurities may be causative of various failures inthe process of sintering. For this reason, most part of themicroparticulate dust and microparticulate sludge with the impuritieshave not been recycled despite of their large contents of usefulelements such as iron, carbon and so forth. For example, zinc containedtherein may vaporize and disseminate, contained in the exhaust gas,adhere to a heat-resistance grate, and cause clogging. Alkali containedtherein may worsen dust collection efficiency of a dust precipitator,and increase suspended particle concentration. Oils contained thereinmay be causative of sudden combustion of an electric dust precipitator,so that the amount of use is strictly limited.

On the other hand, there has been proposed a method of sintering usingLD converter dust as the main raw material, typically in PatentDocument 1. The technique makes use of exothermic effect of metal ironcontained in the LD converter dust.

Patent Document 2 proposes updraft sintering (upward suction type)method, by which the LD converter dust is sintered while being removedwith zinc (see FIG. 3).

Non-Patent Document 1 proposes, as a technique of consuming a largeamount of iron ore particles having a particle size of several hundredsof micrometers, a method of granulating a microparticulate raw material(approximately 60%) and a nucleus material using preliminarily a drummixer or disk pelletizer.

Similarly, as a technique of using a large amount of microparticulateiron ore, there is also provided a method of mixing 40% ofmicroparticulate raw material to a common raw material for sintering(ore powder 60%), granulating the mixture using a disk pelletizerbesides drum mixer to produce pellets of 5 to 10 mm, adding coke fines,and then sintering the pellets coated with coke.

Patent Document 4 proposes, as one technique of enhancing granulation, avibration kneading granulation process by which a large number ofcompaction media are housed in a vessel, and allowing microperticulateraw material added with water to granulate in the vessel under anacceleration of circular vibration of 3 to 10 G (G: acceleration ofgravity). This technique is reportedly effective when fine ore having agrain size of smaller than 63 μm is granulated to as much as 80% ormore.

[Patent Document 1] Japanese Patent Application Laid-Open No.2000-248320

[Patent Document 2] Japanese Patent Application Laid-Open No. H10-330851

[Patent Document 3] Japanese Patent Application Laid-Open No. H8-193226

[Patent Document 4] Japanese Patent Application Laid-Open No. H3-166321

[Non-Patent Document 1] “Shoketsu Genryo no Zoryu to sono Yakuwari(Granulation of Raw Material for Sintering and Roles Thereof”,Tetsu-to-Hagane, Vol. 71, No. 10 (1988)

SUMMARY OF THE INVENTION

However, the sintering method disclosed in Patent Document 1 making useof exothermic effect of metal iron contained in LD converter dust isapplicable only to the cases where the content of metal iron is large.

The updraft sintering disclosed in Patent Document 2 is operable onlyunder narrow conditions of sintering strictly limiting thickness ofsintering layers and wind velocity through sintering bed. Therefore, themethod is not adoptable to the entire kind of the microparticulate dustand microparticulate sludge, either by the downdraft system or theupdraft system, and cannot be understood as a method allowing stablesintering under general conditions of sintering.

The technique using a large amount of fine iron ore, disclosed inNon-Patent Document 1, needs additional facilities other thanmixer-granulator used for conventional sintering process, and has notbeen practiced from the economical viewpoint. Moreover, effects of thetechnique are not so clear, because the granulation strength is low, anda large part of them may collapse during transportation period after thepreliminary granulation, through the mixer-granulator, up to arrival atthe sintering machine. It may be said that such technique cannotdirectly be applicable to the microparticulate dust and microparticulatesludge, which are inferior to fine iron ore in terms of granulability,and conclusively cannot be put into practical use.

No practical and commercial cases have been known with respect tosintering of the microparticulate dust and microparticulate sludge usingthe vibration kneading granulation process, capable of enhancinggranulation, disclosed in Patent Document 4. Experiments by the presentinventors actually using the microparticulate dust and microparticulatesludge proved that the sintering was strong to a certain degree, but wasnot stable.

As has been described in the above, the total production of themicroparticulate dust and microparticulate sludge could not have beenrecycled by the prior art, and the state of things is such that they arecommitted to landfill. Some ironworks may treat them usinghigh-temperature reduction facilities provided besides the sinteringmachine, while raising problems in drastic increase of cost includingenergy consumption, cost of facility, and cost of operation.

However, the microparticulate dust and microparticulate sludge havelarge iron contents, and are preferably recycled rather than beingcommitted to landfill, and may preferably be treated by sintering whichis far more advantageous over the high-temperature reduction in terms ofenergy consumption, cost of facility, and cost of operation.

The present invention is conceived after considering the above-describedsituation, and is to enable sintering using, as main raw materials, themicroparticulate dust and microparticulate sludge which have been usedonly to a limited amount by the methods of sintering at present. Thepresent invention is also to enable an economic andlow-environmental-load(or burden) method of sintering, even if themicroparticulate dust and microparticulate sludge contain impuritiessuch as zinc, alkali and oils.

According to the present invention, there is provided a method ofgranulating raw material for sintering aimed at granulating a rawmaterial for sintering, which includes blending a raw material forsintering of 100% in total, so as to adjust iron-containing dust and/orsludge to 60% or more, and coarse grains having a grain size of 2 mm orlarger to 20% or more on the weight basis, adding thereto one-third orless of the total amount of addition of coke breeze as a fuel, andkneading and granulating the blend using a vibration kneading granulatorto thereby produce granulated grains; and adding the residual portion ofthe total amount of addition of coke breeze to the granulated grains,and subjecting the blend to exterior coating granulation using a rollinggranulator. In this case, sludge produced in a coke plant, or blastfurnace ash may be available as a substitute for a part of, or theentire portion of the coke breeze.

According to the present invention, there is also provided a method ofmanufacturing sintered iron ore based on sintering using a fractionhaving a grain size of 1 mm or larger, out of the raw material forsintering granulated by the method of granulating a raw material forsintering according to the present invention.

In particular, for the case where impurities such as zinc, alkali andoils are contained, the sintering is preferably carried out based onupdraft sintering. The sintering is preferably carried out using arotary-hearth sintering machine with an apparatus of water-seal closedstructure between an exhaust gas system and a pallet of saidrotary-hearth sintering machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is flow chart explaining a method of manufacturing sintered ironore applied with the present invention;

FIG. 2A is a drawing explaining an outline of a rotary-hearth sinteringmachine (DL type machine);

FIG. 2B is a drawing explaining a straight-strand sintering machine (DLtype machine); and

FIG. 3 is a drawing schematically showing a state of proceeding ofsintering based on downdraft ventilation and updraft ventilation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferable embodiments of the present invention will be explained below,referring to the attached drawings.

First, details of how the present inventors reached, after extensiveinvestigations, the method of granulating raw material for sintering anda method of manufacturing sintered iron ore will be explained. Anessential point of the present invention is to provide a method ofgranulating a material for sintering using microparticulate dust andmicroparticulate sludge as main raw materials, and a method ofmanufacturing sintered iron ore, based on an original idea made on amethod of granulation and a method of manufacturing sintered iron orewhile taking sintering characteristics of microparticulate dust andmicroparticulate sludge different from those of iron ore powder intoconsideration.

The present inventors basically analyzed intrinsic causes forincapability of the conventional technique of sintering iron ore, whichcannot sinter a large amount of microparticulate dust andmicroparticulate sludge. Finally, the present inventors found out thatthe fine particles of the microparticulate dust and microparticulatesludge, in particular those having a grain size of 100 μm or smaller,are likely to fluidize by blown air in the process of sintering, andthat such fluidization makes the sintering and binding difficult.

This is because the microparticulate dust and microparticulate sludge,more likely to be free than the common raw materials of conventionalsintering, are more difficult to be kept still, less likely to fuse andbind together even after being heated to sintering temperature, and isconsequently less likely to form a sintered compact. It was made clearthat, as a consequence, the sintering failure is ascribable to that theydisseminate in a form of dust in the exhaust gas, rather than beinggrown into a solid sintered compact even if they should sinter.

Such sintering reaction proceeds in the pallet, so that the state ofproceeding thereof is blinded and hidden in a “black box”. Therefore,the present inventors made an original devise of a specializedtransparent sintering pot for testing, and investigated the appropriatesintering reaction to further details.

A basic condition for stable sintering of the microparticulate dust andmicroparticulate sludge is to prevent the fine particles from being keptin a free state. In the conventional sintering of iron ore powder usinga raw material having a mean particle size of relatively as coarse asthe order of millimeter, the raw material for sintering could besintered anyhow even if it contains a small amount of fine particles,because they are incorporated into quasi-particles, despite somedegradation in the yield and in the productivity in term of sinteringperformance.

For this reason, the raw material blend used at present is sinteredgenerally under a content of 20% or around of iron ore particles as fineas of 1 mm or below. However, increase in the content ofmicroparticulate dust and microparticulate sludge degrades theproduction speed, and the sintering will no more proceed if the contentexceeds 30%. This phenomenon has been well known in general, wherein thepresent inventors found out that the causes for this failure reside inbrittleness of the sintered compact of the particles formed in theprocess of sintering of the microparticulate dust and microparticulatesludge, based on fluidization phenomenon, or nearly under fluidization.

The countermeasure therefor may be such as producing granulated grainsto as strong enough as inhibiting the fluidization of themicroparticulate dust and microparticulate sludge in the process ofsintering, so that an experimental sintering was carried out whileexcluding ungranulated particles from the material for sintering.

After our repetitive experiments aimed at finding out the minimumgranulatable grain size under which the ungranulated particles canstably be sintered, it was made clear that the critical lower limit ofon-screen grain size is 1 mm, and that grains screened through a1-mm-mesh or larger screen can stably be sintered.

It was also made clear from our repetitive experiments that when thegranulated grains which remain on a screen are weak, they may returnback to their free state in the process of sintering, so that thegranulation to as strong enough as preventing them from returning backto their free state is necessary.

It was made clear also that formation of hard granulated grains from themicroparticulate dust and microparticulate sludge is difficult, so faras the conventional rolling type granulation using a drum granulator orpan palletizer is adopted. Mixing granulation such as using Eirich mixerespecially adopted to granulation of iron ore may produce granulatedgrains slightly harder than those obtained by rolling type granulation,but the granulated particles of the microparticulate dust andmicroparticulate sludge were found to give only insufficient strength.

In contrast, it was made clear that granulation based on vibrationacceleration granulation technique, such as using a vibro-explorer, atan acceleration of 6 G or above enabled strong granulation. It was alsomade clear that water in the microparticulate dust and microparticulatesludge is non-uniformly distributed in granulated particles on thespatial basis, so that dry out of the non-uniformly distributed water atdrying temperature during sintering may produce voids where water onceexisted, and may induce collapse and fluidization of the particles. Itwas also found that the granulation proceeded under an acceleration of 6or above, while keeping the water content within a 10% range of theoptimum value, may successfully prevent collapse and fluidization ofparticles.

The present inventors also found out that sintering may stably beproceeded in some cases but may not in other cases, even with an effortof preventing the particles from being set free, and made extensiveinvestigations to find causal factors. As a consequence, it was madeclear that the state of production of molten liquid in the process ofsintering should be controlled as being adapted to the fusingcharacteristics of the microparticulate dust and microparticulatesludge, in view of stable sintering.

Generally, fine particles having an extremely large specific surfacearea, such as the microparticulate dust and microparticulate sludge, arelikely to fuse in the process of sintering, so that an aggregate onlycomposed of the microparticulate dust and microparticulate sludge maymelt down at a time, when it reaches a certain high temperature, so thatit is principally difficult to form and sustain a porous sinteredcompact which is a proper form of sinter product.

In addition, in the general sintering, coarse grains form a solidskeleton, the molten liquid surround the surface of the grains, thecoarse grains bind with each other using the molten liquid as a binder,and thereby the sintered compact is gradually formed in turn as thesintering reaction proceeds. At the same time, the coke breeze containedin the raw material keeps to combust under ventilation during sintering,so that current system of sintering iron ore powder, allowing thesintering to proceed with the aid of this heat, cannot maintain thereaction unless the porous compact body is formed while ensuring thereinformation of through-pores for ventilation.

For an exemplary case where the molten liquid is excessively produced inthe process of sintering, the molten liquid fills up voids between thecoarse grains so as to choke up the ventilation pores, and the sinteringreaction no more proceeds. Therefore, it has been well known thatcontrol of the molten liquid is an essential point in the sinteringoperation.

For this reason, use of a large amount of microparticulate dust andmicroparticulate sludge may be more likely to reduce the ratio of coarseparticles which form the nucleus, to fill up the gaps between the coarsegrains, and to cause choking-up of the ventilation pores if the rawmaterial tends to fuse at a time by its nature. For stable sintering ofa large amount of microparticulate dust and microparticulate sludge, itis therefore necessary to find out a technique of fusion control adaptedto the fusing characteristics of the microparticulate dust andmicroparticulate sludge.

After extensive investigations, the present inventors found out thatsintering of the entire microparticulate dust and microparticulatesludge only by themselves are difficult, that the sintering may bestabilized only when the raw material blend contains coarse grains of 2mm or larger to as much as 20% or more, and that, at the same time, someoriginal idea on combustion control of cokes may be necessary in orderto control production of the molten liquid.

The nucleus-forming coarse grains are contained relatively a largeamount in the raw material blend for sintering used for iron oresintering, but increase in the nucleus-forming material converselydecreases the ratio of blending of the microparticulate dust andmicroparticulate sludge which increase use is target of the presentinvention. In order to ensure the ventilation pores using a possiblyminimum amount of nucleus-forming material, it may therefore benecessary to provide a technique of controlling quantity of moltenliquid, capable of ensuring a certain amount of molten liquid necessaryto make bind structure of sinter, while suppressing melting of thenucleus-forming material.

Production of the molten liquid in the process of sintering, induced bycombustion heat of the cokes, may be controllable to a certain extent bythe amount of addition of cokes, but may be controllable also byalignment of cokes in granulated grains, which is another measure forcombustion control of cokes. One known technique in this field is acokes interior/exterior technique making distribution of cokes differedbetween the inside and outside of the granulated grains.

On the other hand, the amount of cokes may preferably be reduced aspossible when the microparticulate dust and microparticulate sludge aregranulated, because the coke breeze acts to lower the strength of grainsin the process of granulation. After through investigations into optimumoverall conditions for granulation, capable of optimizing production ofmolten liquid of the microparticulate dust and microparticulate sludge,while suppressing the amount of use of nucleus-forming material, thepresent inventors found out that it is necessary, for stable sintering,to suppress the amount of the interior cokes, under theinterior/exterior distribution, to as much as one-third or less of thetotal amount of addition of coke breeze.

Then, at the initial stage of granulation, the total amount ofmicroparticulate dust and microparticulate sludge, added with a part ofcokes (one-third or less of the total amount of coke breeze), aregranulated by vibration kneading granulation, and the granulation iscontinued by adding the residual amount (two-thirds or more of the totalamount of coke breeze) of cokes to the granulated grains so as to coverthe surface thereof. Smaller amount of cokes may be better in theprocess of vibration kneading granulation from the viewpoint ofgranulated particle strength, but the interior cokes may be reduced onlyto a certain lower limit from the viewpoint of production of moltenliquid, indicating existence of an optimum range with respect to theratio of the amount of interior/exterior cokes.

As raw material of the nucleus-forming coarse grain may be availablereturned sinter fines, or may be coarse grains of iron ores or limestone. The coke breeze added as a fuel may be used as it were because ithas conventionally been applied to sintering of iron ore, but a part of,or entire portion of which may be substituted by sludge produced in cokeplants, or by blast furnace fly ash.

Specifically summarizing now the above-described method, sintering usingthe microparticulate dust and microparticulate sludge as the main rawmaterial may be practiced by carrying out the processes shown in FIG. 1.

First, a raw material for sintering of 100% in total is blended so as toadjust iron-containing dust and/or sludge to 60% or more, and coarsegrains having a grain size of 2 mm or larger to 20% or more on theweight basis, one-third or less of the total amount of addition of cokebreeze as a fuel is added thereto, and the blend is kneaded andgranulated using a vibration kneading granulator to thereby producegranulated grains (step S1). The ratio of blending herein is expressedon the dry weight basis. For the rest of 100% in total of the rawmaterial to be sintered, conventional iron-containing raw material forsintering such as iron ore powder, returned sinter fines and so forth,may be used.

Next, the residual portion of the total amount of addition of cokebreeze is added to the granulated grains granulated in step S1 in theabove, and the blend is subjected to exterior coating granulation usinga rolling type granulator (step S2).

The raw material for sintering, granulated by the granulation processesin steps S1, S2 described in the above, is sieved, and a fraction havinga grain size of 1 mm or larger is used for sintering (step S3).

As has been described in the above, stable sintering using themicroparticulate dust and microparticulate sludge as main raw materialsmay be realized, by keeping the ratio of content of the nucleus-formingmaterial in the raw material blend for sintering within a certain level,by carrying out cokes interior/exterior granulation while keeping theratio of interior/exterior cokes at a certain condition, and by usingonly strong granulated grains containing no fraction having a grain sizeof 1 mm or smaller. The conventional sintering of iron ore could notstably sinter the raw material containing 30% or more ofmicroparticulate dust and microparticulate sludge, whereas by adoptingthe conditions for sintering described in the above, it became feasibleto stably sinter the raw material even if the microparticulate dust andmicroparticulate sludge are blended to as much as 60% or more. As hasbeen described in the above, sintered iron ore is now producible withhigh efficiency making use of the conventional facility, by using themicroparticulate dust and microparticulate sludge produced as by-productin ironworks, extremely small in grain size, hard to granulate and hardto sinter, which are intrinsically different from sinteringcharacteristics of ordinal iron ore, and by sintering the raw materialby a method of sintering completely different from theconventionally-adopted methods of sintering.

By the way, some microparticulate dust and microparticulate sludge maycontain impurities allowing manufacturing of sintered iron ore, but somemay obstruct sustenance of stable production of sintered iron ore. Ashas been described in the above, zinc contained therein may form zincwhite and may vaporize into the exhaust gas in the process of sintering,and may clog grate, or may adhere on an exhaust pipe, a dustprecipitator or a blower, to thereby obstruct proceeding of operation.The alkali metals contained therein may not only degrade the dustcollection efficiency of electric precipitator, but may also becausative of increase in the amount of emission of suspended particlesthrough a chimney out into the air, and may therefore not be adoptableas the raw material for sintering. The oils contained therein may becausative of sudden combustion of an electric dust precipitator, and maybe causative of adhesion of uncombusted oils onto the blower, so thatthe oils may be adoptable only to as much as a certain limited amount.

The present inventors went into through investigations to solve theabove-described problems, and finally reached a method capable ofsintering a large amount of particulate dust and microparticulate sludgecontaining impurities, which could have not been used up to a largeamount by the conventional method of sintering. The details will bedescribed below.

The reason why the microparticulate dust and microparticulate sludgecontaining impurities cannot be used is that the sintering machine has adowndraft configuration, having the dust precipitator and the suctionblower arranged in the exhaust system, and this may be causative offailure. To solve this problem, the method of sintering may need amechanism in which the exhaust system is provided independently from thegrate, blower and so forth, so as to protect the individual facilitiesfrom various failures ascribable to the impurities in the exhaust gas.

The updraft sintering is a method by which sintering is proceeded whileintroducing the air compressed by the blower in an air box under palletof the sintering machine, and blowing, under pressure, the air upthrough the grate of the pallets bottom. By the method, the exhaust gasdissipates from the top surface of the pallets of the sintering machine,so that impurities such as zinc, alkali, uncombusted oils and so forth,even if contained therein, will never be brought into contact with thegrate nor the blower, inducing no failures. A device removing theseimpurities may also be provided as being brought into direct contactwith the exhaust gas system, by which the impurities may efficiently beremoved.

In general, stable sintering is more difficult in the updraft sinteringthan in the downdraft sintering. In the downdraft sintering, thesintered compact is produced while the molten liquid in the downdraftsintering gradually flows down by gravity, whereas in the updraftsintering, the particles become more difficult to fuse, because themolten liquid cannot move upward. In particular, the microparticulatedust and the microparticulate sludge are likely to fluidize by a rapidair flow passing through the sintering layer at a speed of severalmeters per second, making fusion binding (or sintering) difficult. Inthe updraft sintering proceeded under more severe sintering conditionsthan in the downdraft sintering, adoption of the method of granulatingraw material for sintering and the method of manufacturing sintered ironore of the present invention using the microparticulate dust and themicroparticulate sludge, which are hard to sinter, as main raw materialsis very effective, and thereby stable sintering may be realized usingthe impurity-containing microparticulate dust and the microparticulatesludge as main raw materials.

Most of updraft sintering machines generally have a straight-typestrand, wherein movable pallets and a strand frame are brought intocontact on a rail at mechanical sliding portions while ensuring only alimited degree of air-tightness, causing a considerable air leakage andnoise. The air leakage is also causative of unnecessary consumption ofelectric energy of the blower.

As shown in FIG. 2B, the strand is configured so as to allow the palletsP to move in an endless manner. Because the route of return pallets liesbelow the strand, the eaves height of facility becomes large, and notonly increases costs of facility, but also makes the machine incapableof suppressing dust. Since the pallets P tends to cause heavy materialfatigue under repetitive heating load, a steel of expensive quality isused therefor.

In order to configure a sintering machine solved in the above-describedproblems, small in environmental load, and suppressed in costs offacility and operation, it may be necessary from the view point ofmechanism that the sintering machine would have no return pallets.Although conventionally been configured as a straight line type, now thesintering machine may be configured as rotary-hearth type asschematically shown in FIG. 2A, by which the return pallets may beomissible, and the air box and the pallets P and the frame may beintegrated. Accordingly, the air leakage may completely be avoidable,and extremely clean sintering as compared with the conventionalsintering machine, completely suppressed in dust generation from thereturn pallets, may be realized.

The rotary-hearth sintering machine is suitable as a sintering machinedisusing the return pallets, and may be applicable both to the downdraftsintering and the updraft sintering. Sintering using, in particular, themicroparticulate dust and microparticulate sludge as the main rawmaterials has suffered from heavy dust generation, and large air leakagedue to increased ventilation resistance, thereby the conventionalsintering machine having the return pallets has been limited inperformance. Placing this point into focus, adoption of therotary-hearth system to the method using the microparticulate dust andmicroparticulate sludge as main materials may be effective, and mayrealize sintering suppressed in problematic dust generation and noisefrom the sintering machine, moderated in the environmental load, loweredin the cost for facility, reduced in the air leakage, and reduced in theunit consumption of electricity.

If the rotary-hearth system is used in the updraft sintering, therotating pallets and a stationary exhaust gas system may be sealed usinga water-seal device, and thereby the exhaust gas may be confined (seePatent Document 3). Adoption of this technique allows simple operationof exhaust gas processing, because the exhaust gas system thereof has noblower provided therein, unlike the downdraft sintering system. Adoptionof this technique is extremely effective in particular to treatment ofexhaust gas generated from sintering of microparticulate dust andmicroparticulate sludge containing impurities such as zinc oxide, alkalimetals, uncombusted oils and so forth.

EXAMPLE 1

One hundred percent in total of a raw material to be sintered was madeup by 80% of LD converter dust, and 20% of coarse returned sinter fines.One percent (percentage (dry weight) assuming the amount of raw materialto be sintered as 100) of blast furnace secondary fly ash was externallyadded thereto as a fuel, the blend was kneaded and granulated for 4minutes using a vibration kneading granulator, further added with 3%(percentage (dry weight) assuming the amount of raw material to besintered as 100) of blast furnace secondary fly ash, and subjected torolling type granulation using a pan pelletizer. The granulated grainswere then allowed to pass through a 3-mm-mesh vibration screen device,and those of 1 mm or larger were charged into a rotary-hearth sinteringmachine for updraft sintering. Since the grains contain zinc dust, theportion between the exhaust gas system and the pallets of the sinteringmachine was configured by a water-seal closed structure, coarse dust inthe exhaust gas was then removed using a cyclone dust collector,followed by rapid cooling. Zinc oxide is then recovered using a zincoxide collector, and the exhaust gas was emitted out into the air afterdust removal using a bag-filter dust collector.

EXAMPLE 2

One hundred percent in total of a raw material to be sintered was madeup by 35% of oil-containing sludge, 45% of lime sludge, and 20% ofcoarse return fines. Three percent (percentage (dry weight) assuming theamount of raw material to be sintered as 100) of coke breeze wasexternally added thereto as a fuel, the blend was kneaded and granulatedfor 4 minutes using a vibration kneading granulator, further added with6% (percentage (dry weight) assuming the amount of raw material to besintered as 100) of coke breeze, and subjected to rolling typegranulation using a pan pelletizer. Granulated grains of 1 mm or largerwere collected through a vibration screen device, and then subjected toupdraft sintering using a rotary-hearth sintering machine. The portionbetween the exhaust gas system and the pallets of the sintering machinewas configured by a water-seal closed structure, coarse dust in theexhaust gas was then removed using a cyclone dust collector, and theexhaust gas was emitted out into the air after cleaned through a porousactivated cokes packed layer.

EXAMPLE 3

One hundred percent in total of a raw material to be sintered was madeup by 45% of iron-containing dust 45%, 15% of iron-containing sludge, 5%of waste powder from iron ore, and 25% of return fines. One-and-a-halfpercent (percentage (dry weight) assuming the amount of raw material tobe sintered as 100) of coke breeze was externally added thereto as afuel, the blend was kneaded and granulated for 4 minutes using avibration kneading granulator, further added with 4% (percentage (dryweight) assuming the amount of raw material to be sintered as 100) ofcoke breeze, and subjected to rolling type granulation using a panpelletizer. Granulated grains of 1 mm or larger were collected through avibration screen device, and then subjected to sintering using adowndraft DL (Dwight-Lloyd) sintering machine.

EXAMPLE 4

One hundred percent of 5%-oil-containing sludge (fine particulate scale)was used as a raw material, and kneaded for 4 minutes using a vibrationkneading granulator without being added with fuel, granulated grains of1 mm or larger was collected through a vibration screen device, andallowed to sinter using a rotary-hearth updraft sintering machine. Theexhaust gas containing dioxin was prevented from being emitted into theair by providing a water-seal closed structure to the portion betweenthe exhaust gas system and the pallets of the sintering machine, andemitted through a porous activated coke packed layer after being removedwith dust using a cyclone dust collector and a bag filter.

INDUSTRIAL APPLICABILITY

The present invention enables high efficiency sintering usingmicroparticulate dust and microparticulate sludge, which are small ingrain size, less likely to be granulated, and difficult to sinter, asmain raw materials, using a conventionally-used sintering facility.

1. A method of manufacturing sintered iron ore based on sinteringwherein the method comprises: (1) granulating a raw material forsintering by: (a) blending a raw material for sintering of 100% intotal, so as to adjust iron-containing dust and/or sludge to 60% ormore, and coarse grains having a grain size of 2 mm or larger to 20% ormore on the weight basis, adding thereto one-third or less of the totalamount of addition of coke breeze as a fuel, and kneading thegranulating the blend using a vibration kneading granulator to therebyproduce granulated grains; and (b) adding the residual portion of thetotal amount of addition of coke breeze to said granulated grains, andsubjecting the blend to exterior coating granulation using a rollinggranulator to produce a granulated raw material for sintering; and (2)screening the granulated raw material for, sintering to produce afraction having a grain size of 1 mm or larger; and (3) sintering thefraction having a grain size of 1 mm or larger to produce sintered ironore.
 2. The method of manufacturing sintered iron ore according to claim1, wherein sludge produced in a coke plant, or blast furnace ash isavailable as a substitute for a part of, or the entire portion of saidcoke breeze.
 3. The method of manufacturing sintered iron ore accordingto claim 1, wherein the sintering is updraft sintering.
 4. The method ofmanufacturing sintered iron ore according to claim 2, wherein thesintering is updraft sintering.
 5. The method of manufacturing sinterediron ore according to claim 1, wherein the sintering is carried outusing a rotary-hearth sintering machine.
 6. The method of manufacturingsintered iron ore according to claim 2, wherein the sintering is carriedout using a rotary-hearth sintering machine.
 7. The method ofmanufacturing sintered iron ore according to claim 3, wherein thesintering is carried out using a rotary-hearth sintering machine.
 8. Themethod of manufacturing sintered iron ore according to claim 4, whereinthe sintering is carried out using a rotary-hearth sintering machine. 9.The method of manufacturing sintered iron ore according to claim 5,wherein a portion between an exhaust gas system and a pallet of saidrotary-hearth sintering machine has a water-seal closed structure. 10.The method of manufacturing sintered iron ore according to claim 6,wherein a portion between an exhaust gas system and a pallet of saidrotary-hearth sintering machine has a water-seal closed structure. 11.The method of manufacturing sintered iron ore according to claim 7,wherein a portion between an exhaust gas system and a pallet of saidrotary-hearth sintering machine has a water-seal closed structure. 12.The method of manufacturing sintered iron ore according to claim 8,wherein a portion between an exhaust gas system and a pallet of saidrotary-hearth sintering machine has a water-seal closed structure. 13.The method of manufacturing sintered iron ore according to claim 1,wherein said coarse grains are returned sinter fines, coarse grains ofiron ores or limestone.